Gasification device

ABSTRACT

A gasification device is described for the introduction of a gas into a liquid, in particular of air into waste water.  
     The gasification device comprises a blower body element, which carried a membrane made of an elastic material with perforation slits.  
     The gasification device contains means arranged in an area located at the top, related to the installation location, which, with the gas feed switched off and the hydrostatic pressure of the waste water imposed, necessarily causes the formation of an axial fold of the membrane in this upper area. This area is, at the same time, free of perforation slits.

[0001] The invention relates to a gasification device according to thepreamble to claim 1.

[0002] A gasification device of this generic type is known from DE-PS 3819 305. A blower body element of this gasification device is made of aplastic and the membrane of an elastomer. The membrane features bothareas with perforation slits through which the gas can pass into thewaste water which is to be treated, i.e. also into areas withoutperforation slits, e.g. directly at a gas distribution slot, in order toprevent an indirect and excessively concentrated emergence of gas atthat point.

[0003] The basic design of this known gasification device has been triedand tested. With regard to the selection of the material for themembrane, considerable progress has been made recently, which haslargely succeeded in reducing deposits of slime and encrustations byorganic and inorganic content substances as well as losses of softener.The possibly longer service life which is inherently possible with thisprogress is, however, limited again by the fact that mechanical damagecan occur to the membrane due to cracks which did not previously occurdue to the earlier replacement required of the membrane.

[0004] The objective on which the invention is based is to extend stilllonger the service life of the membrane of a gasification device of thetype referred to in the preamble by reducing the propensity to crackformation.

[0005] This objective is achieved with a gasification device accordingto the preamble to claim 1, by the features described in thecharacterisation section.

[0006] Further designs and advantageous embodiments are described in thesub-claims.

[0007] The solution according to the invention required in the firstinstance extensive investigations into causes, which was rendered moredifficult by the fact that a gasification device cannot be monitored inpractical operation. In this context, the following was discovered:

[0008] Crack formation occurs in particular if the gasification deviceis not operated continuously but intermittently. The reason for thisintermittent gas introduction is the treatment concept in clarificationplants for a number of types of waste water. This is based initially onexploiting the ability of bacteria, predominantly aerobic bacteria, toaerate organic substances, i.e. to break them down in the final analysisinto carbon dioxide, water, nitrates and sulphates. A precondition forthis in aerobic operating systems is an adequate aeration of theactivated sludge in the waste water. The aeration is then stopped andthe biological waste water purification with anaerobic agents, i.e.bacteria which live off chemically-bonded oxygen and therefore carry outreductive decomposition, increases in importance.

[0009] Due to intermittent operation, pauses arise in which no gas isintroduced into the waste water, and the membrane is then no longerinflated by a gas cushion between its inner side and the outer side ofthe blower body element, to form a fold in the upper part of themembrane. The research into the causes identified the following reasonsfor this:

[0010] When the aeration process is switched off, the hydrostaticpressure in the waste water of the clarification plant has the effect ofpressing the membrane against the blower body element. However, becausethis does not always take place uniformly it is possible thatuncontrolled fold formation takes place, which runs into the area of theperforation slits, and there gradually leads to the fatigue of thematerial.

[0011] Specifically, the area of the membrane with the perforation slitsis some less stiff than the remaining unperforated area, and thereforetends to initiate uncontrolled fold formation in the perforated area forpreference, or continues therein. Once a fold has started in that area,it continues to develop at the same point. However, the perforationslits already represent a weakness in the material, and favour thetearing of the membrane as the fatigue of the material progresses.

[0012] The effect described of fold formation is further favoured if themembrane is “oversize”; i.e. its circumference in the relaxed state isgreater than the circumference of the blower body element. This isfrequently the case in practice, since an oversize which is alreadypresent at manufacture facilitates fitting, since the membrane can betautened without resistance over the blower body element. In addition tothis, a sustained expansion of the membrane occurs with time duringoperation due to the imposition of pressure from within.

[0013] With the gasification device according to the invention,uncontrolled fold formation is avoided, in that a controlled foldformation is forced into effect. In this situation, the controlled foldformation is effected in an area of the membrane which is free ofperforation slits and therefore not already weakened. Once a foldoccurs, therefore, the “excess” material which is present because of theoversize can dam up the circumference of the membrane in this fold, withthe result that there is no opportunity for further fold formation at anundesirable point. Accordingly, the other areas of the membrane, inparticular the areas with the perforation slits, can lie smoothlyagainst the blower body element under the effect of hydrostatic pressurewhen the gas feed is switched off, and is therefore not subjected tofolding.

[0014] The arrangement of the fold-forming material in an upper area,related to the installation position, makes use of the tendency alreadypresent towards uncontrolled fold formation in the upper half of thegasification device. In this situation a part is played by the fact thatthe hydrostatic pressure in the lower part is less than in the upperpart, and the membrane accordingly is initially in contact at the bottomof the blower body element when the gas feed is switched off, and thenby and by further up.

[0015] Without the means according to the invention, however, thisprocess would not take place exactly uniformly, since flows in the wastewater also play a part, and the forces resulting from this aresuperimposed on the hydrostatic pressure. It is then possible for foldsto form beneath the crest, in other words the highest-lying line of themembrane, which has indeed been demonstrated to be the case in practice.

[0016] According to a further embodiment, the means can be formed by alongitudinal section of the membrane with an impressed camber radiuswhich is smaller than the mean camber radius of the membrane measured inthe state as fitted on the blower body element.

[0017] The hydrostatic forces which take effect radially on the membranewhen the gas feed is switched off then support the inclination towardsfold formation, already incurred, of the more sharply cambered area ofthe membrane.

[0018] As an alternative, the means can also be provided by alongitudinal ridge, which projects over the circumference of the casingsurface of the blower body element.

[0019] The advantage of this design lies in the fact that it is possibleto do without a special preliminary deformation of the membrane. Becausein this case too the membrane, when contracted, is in the first instancemore cambered at one point than in the other areas, the same effect ofthe hydrostatic forces taking effect radially on the membrane is thenexploited which also leads to the fold formation at the desired pointwith the pre-deformed membrane.

[0020] Several variants are possible with the design and arrangement ofthe longitudinal ridge; for example, the ridge can be an integral partof the blower body element.

[0021] This requires a modification of the manufacturing mould incomparison with the conventional design. With subsequent manufacture,however, no relevant additional costs are incurred, since the fitting ofthe membrane to the blower body element can take place without change.

[0022] In addition, the longitudinal ridge may also be a separatecomponent, which can be inserted between the membrane and the blowerbody element.

[0023] With this design, it is possible to do without a modification tothe manufacturing mould, although an additional working stage isrequired during assembly. It may also be necessary for the longitudinalridge to be fixed to the blower body element.

[0024] A further embodiment makes provision for the longitudinal ridgeto be secured on the side of the membrane which faces inwards. It istrue that in this case, too, it is possible to do without themodification of the manufacturing mould for the blower body element, butan additional working stage is nevertheless still necessary.

[0025] The longitudinal ridge can also be arranged on the inwards facingside of the membrane and be an integral part thereof.

[0026] With this embodiment, a modification to the mould for themanufacture of the membrane is necessary; otherwise, however, norelevant additional costs are incurred in the subsequent installation.

[0027] In a further embodiment, the means can be formed by alongitudinal area of the membrane with an impressed camber radius, whichprovides a camber directed inwards in relation to the blower bodyelement.

[0028] In this context, the camber radius is smaller than the meancamber radius of the membrane when measured in the state as mounted onthe blower body element.

[0029] When the gas feed is turned off, the hydrostatic forces takingeffect radially on the membrane cause a fold formation in thepre-treated longitudinal section of the membrane. In this situation thecamber radius in the centre of this longitudinal section increases,while the laterally delimited areas likewise form folds, although withthe camber in the opposite direction.

[0030] Finally, it is possible for a longitudinal groove to be arrangedin the blower body element in the area of the longitudinal area of themembrane.

[0031] The longitudinal groove allows for a deflection inwards of theincreasing crest of the longitudinal area, under the influence of thehydrostatic pressure, in relation to the blower body element.

[0032] The invention is explained hereinafter on the basis of thedrawings.

[0033] The drawings show:

[0034]FIGS. 1a-c A cross-section through a gasification device with apreformed membrane of a camber directed outwards in three contractionphases,

[0035]FIGS. 2a-c A cross-section through a gasification device with aridge in three contraction phases,

[0036]FIGS. 3a-c A cross-section through a gasification device with apreformed membrane, with a camber directed inwards in three contractionphases, and

[0037]FIGS. 4a-c A cross-section through a gasification device accordingto FIG. 3, with an additional longitudinal groove in the blower bodyelement, in three contraction phases.

[0038] FIGS. 1 to 4 show cross-sections through a gasification device10. The gasification device 10 consists of a blower body element 12 anda membrane 14 surrounding this. The membrane 14 features areas 16 withperforation slits 18 for the introduction of a gas into the fluid, andfurther areas 22, 26, in which no perforation slits are present. Thearea 26 covers a groove 28 running longitudinally in the blower bodyelement 12, which serves to carry out the longitudinal distribution ofthe gas being introduced. The reason for the absence of the perforationslits in this area is to prevent the indirect emergence of the gas beingconducted via the groove 28 through the covered membrane 14 in the areaof the groove. Rather, the intention is to create an overpressure, whichwill raise the membrane 14 with the formation of an annular space for acircumferential gas distribution of the blower body element 12, and, asa result, makes possible the access of the gas to all perforation slits18 and therefore an outlet over a larger surface area.

[0039] While the groove 28 and the area 26 of the membrane 14 whichcovers it, without perforation slits, are located on the bottom byrelation to the installation position of the gasification device 10, afurther area 22, likewise without perforation slits, is locatedopposite, in other words, on the top in relation to the installationposition.

[0040] In this case means 20 are provided which, with the gas feedswitched off and the hydrostatic pressure of the waste water beingpresent, an axial fold of the membrane 14 is mandatorily formed in thisupper area 14.

[0041] With the embodiments according to FIG. 1, these means 20 areformed by a longitudinal area 32 of the membrane 14 with am impressedcamber radius which is smaller than the mean camber radius of themembrane 14, measured in the fitted state on the blower body element 12,and is directed outwards.

[0042] In the embodiments according to FIG. 2, the means 20 are formedby a longitudinal groove 24, which projects over the circumference 30 ofthe casing surface of the blower body element 12.

[0043] The embodiment according to FIG. 3 shows a longitudinal area 34of the membrane 14, in which an impressed camber radius is formed, whichrepresents a camber directed inwards in relation to the blower bodyelement. In view of the fact, however, that in this case the crest whichis formed in this case cannot deviate, additional folds form in theadjacent lateral area, but with the camber facing in the oppositedirection. The superfluous circumference of the membrane in this case isdivided onto three folds.

[0044] The embodiment according to FIG. 4 is based on a membrane 14,such as is also represented in FIG. 3. In addition, the embodimentaccording to FIG. 4 also comprises a longitudinal groove 36 in the areaof the longitudinal area 34 of the membrane 14. The impressed crest canbe deflected inwards into this longitudinal groove 36 under theinfluence of the hydrostatic pressure.

[0045] The longitudinal area 32 with the camber directed outwards, thelongitudinal ridge 24, and the longitudinal area 34 with the camberdirected outwards, if appropriate in combination with the longitudinalgroove 36, have the effect that the membrane 14, initially expandedunder the overpressure, and then contracted with the subsequentdisconnection of the gas feed, initially bends somewhat more markedly onthe tendential crest than at other points. This manifestation thenfavours the formation of folds at this point, which, due to the portionof the hydrostatic pressure becoming greater, finally leads to onesingle emphasised fold.

[0046] Parts a, b, and c of FIGS. 1 to 4 show a number of individualcontraction phases. Part a shows the almost expanded state, in which,however, a fold formation is already indicated in the crest of the upperarea 22 of the membrane 14.

[0047] Part b shows a transitional state, in which the impressing of thefold is forced, and Part c finally shows the end state, in which the“superfluous” circumferential material of the membrane 14 is stored inthe fold, while all other areas are located directly at the blower bodyelement.

1. Gasification device (10) for the introduction of a gas into a liquid,in particular of air into waste water, with at least one blower bodyelement (12), which comprises a membrane (14) made of an elasticmaterial, provided in the area (16) with perforation slits (18) for theintroduction of the gas into the liquid, characterised in that thegasification device (10) comprises means (20), arranged in an upper area(22), by relation to the installation location, which, with the gas feeddisconnected and the hydrostatic pressure of the waste water imposed,force the creation of an axial fold of the membrane (14) in this upperarea (22), which at the same time is free of perforation slits. 2.Gasification device (10) according to claim 1, characterised in that themeans (20) are formed by a longitudinal area (32) of the membrane (14)with an impressed camber radius, which is smaller than the mean camberradius of the membrane (14), measured in the state as mounted on theblower body element (12), and features a camber directed outwards,related to the blower body element.
 3. Gasification device (10)according to claim 1, characterised in that the means (20) are formed bya longitudinal ridge (24), which projects beyond the circumference (30)of the casing surface of the blower body element (12).
 4. Gasificationdevice (10) according to claim 3, characterised in that the longitudinalridge (24) is am integral component of the blower body element (12). 5.Gasification device (10) according to claim 3, characterised in that thelongitudinal ridge (24) is a separate component, which can be locatedbetween the membrane (14) and the blower body element (12). 6.Gasification device (10) according to claim 3, characterised in that thelongitudinal ridge (24) is secured to the inwards-facing side of themembrane (14).
 7. Gasification device (10) according to claim 3,characterised in that the longitudinal ridge (24) is arranged on theinwardsfacing side of the membrane (14) and is an integral part thereof.8. Gasification device (10) according to claim 1, characterised in thatthe means (20) are formed by a longitudinal area (34) of the membrane(14) with an impressed camber radius, which features a camber directedinwards in relation to the blower body element.
 9. Gasification device(10) according to claim 8, characterised in that the camber radius issmaller than the mean camber radius of the membrane (14) in the state asmounted on the blower body element (12).
 10. Gasification device (10)according to claim 8 or 9, characterised in that a longitudinal groove(36) is arranged in the introduction element body (12) in the vicinityof the longitudinal area (34) of the membrane (14).